Waveform Design Using Coprime Frequency-Modulated Pulse Trains for Reverberation Suppression of Active Sonar

Abstract

Over the last two decades, low-frequency active sonar has become an attractive tool for underwater target detection. The reverberation to signal ratio (RSR) of transmitted waveforms is an important factor affecting the detection capability of low-frequency active sonar. Therefore, reasonable waveform design for reverberation suppression of active sonar is an important topic. Pulse trains of linear frequency-modulated (PTFM) waveforms have been proposed and manifested their good performance in suppressing reverberation. The number of sub-pulses is positively related to the reverberation to signal ratio; the lower the number of sub-pulses, the lower the reverberation to signal ratio. However, to avoid ambiguity in a Doppler measurement, the PTFM waveforms have a requirement for the number of sub-pulses to be satisfied, which prevents its reverberation suppression performance from being further improved. In this paper, we propose a coprime pulse train of linear frequency-modulated (CPTFM) waveform, which reduces the number of sub-pulses to some extent. Therefore, the ability of reverberation suppression of the CPTFM waveform can be improved. The RSR was chosen as the metric to evaluate the waveform’s ability to suppress reverberation, and the theoretical formula for the RSR of the CPTFM waveform was derived in zone A and B. With the overlap of zones A and B brought about by the decrease in the number of sub-pulses, the average RSR of zones A and B is used in this paper to evaluate the reverberation suppression ability of the waveform. The simulation experiment shows that the proposed CPTFM waveform decreases the average RSR by 7 dB and 20 dB in comparison to the reference PTFM waveform and continuous waveform (CW), which is consistent with the theoretical results by the derived formulas.

Analysis of Bottom Reverberation Intensity Under Beam-Controlled Emission Conditions in Deep Water

“…2. The material of the seabed is fine sand, with a sound speed of 1753 m/s, a density of 1.957 g/cm 3 , and an attenuation coefficient of 0.51 dB/m ⋅ Hz. To compare the changes in the sound field distribution caused by beam-controlled emission, simulation calculations were conducted using the BELLHOP (Porter, 2011) ray model sound field calculation program, and sound field distributions were given for omnidirectional and directional source emission cases.…”

“…Reverberation is the primary background interference in the active sonar target detection, and a comprehensive understanding of its characteristics and formation mechanism is the key to improving the performance of the active target detection (Cui et al, 2023;Hao et al, 2023). Meanwhile, reverberation carries hidden ocean information that can be used for environmental parameter inversion, leading to the increasing attention toward reverberation research in the field of marine acoustics.…”